Workpiece handling device



Ton.

l A. U. HAANES WORKPIECE HANDLING DEVICE A Aug. 9, 1960 v5 Sheets-Sheet 1 Filed May 26, 1955 Aug. 9, 1960 A. U. HAANEs woRxPIEcE Hmmm Dmc@ 5 Sheets-Sheet 2 Filed May 26, 1955 INVENTOR.

Aug. 9, 1960 Filed May 26, 1955 A. U. HAANEs v WORKPIECE HANDLING DEVICE 3 Sheets-Sheet 3 7o lo s2 "i l 36 44 I le LNX -II 60 o ll I l.4 4 mi 6 b 1` 1 l I l2 INVENTOR ARNT U. HAANES ATTORNEY United States I)attentC) WORKPIECE HANDLING DEVICE Amt U. Haanes, 522 S. Laurel Ave., Royal Oak, Mich. Filed May 26, 1955, Ser. No. 511,280 "1 Claim. (Cl. 214-1) machine, such as a punch press or stamping press, liftv the workpiece out of the die cavity and transfer it to a new precisely-located position at a predetermined level, at which position it may be carried away by a conveyor or picked up by other apparatus beyond the scope of thel present invention. v

Another object is to provide a workpiece handling device of the foregoing character which may be'supported either from the floor or other position beneath the level of the workpiece in the dies or from the ceiling or other position above that level.

Another object is to provide a workpiece handling device of the foregoing character wherein the workpiece can be subjected either to a high lift or a low lift, de pending upon the working conditions, without greatly altering the construction of the device.

Another object is to provide a workpiece handing 'device of the foregoing character wherein the workpiece is grasped by a. gripping jaw attached to an arm which in turn is mounted o'n parallel links pivoted to a vertically movable slide block, a combined swinging and lifting motion being imparted thereto by a crank mechanism preferably actuated by -a motor or other source of power.

Other objects and advantages of the invention will become apparent during the course of the following description of the accompanying drawings, wherein;

Figure l is a side elevation of a workpiece handling device, according to one formy of the invention, with the starting position of the workpiece shownA in solid lines and the finishing position in dotted lines, the paths of travel of the parallel links and their upper pivots being shown in dotted lines; Y v e Figure 2 is a top plan view of the workpiece handling device shown in Figure l; j Y

Figure 3 is a vertical cross-section taken along the line 3 3 in Figure 1;v

Figure 4 is a fragmentary side elevation at the lower ends of the parallel links and the slide block on which they are mounted, taken along the line 4-4 in Figure 3;

`Figure 5 is a side elevation of a modified workpiece handling vdevice arranged for mounting on the ceilingror other overhead position; A

Figure 6 is a diagrammatic vview illustrating the paths ofswing and travel of the principal elements in the oorfmounted workpiece handling device of Figure l;

Figure 7 is a diagrammatic view Villustrating the vpaths of swing and .travel of the `principal `elements in the ceiling-mounted workpiece* handling device .of Figure 45, hen-the crank thereofislengthened and relocated;

further modification of the invention in which the link support oscilates on a swinging arm;

Figure 9 is a View similar to Figure 4 of another modi-l cation wherein the link support is stationary and the links are swung by a lost motion connection between the crank and one of the links;

Figure 10 is a side elevation of a still further modication of the invention; and

`Figure l1 is a right-hand end elevation of the workpiece handling device of Figure 10.

Referring to the drawings in detail, Figures 1 to 4 inclusive and 6 show a floor-mounted workpiece handling device, generally designated 10, according to one form of the invention, as supported on a base 12 resting upon the floor F and having three spaced uprights 14, 15. and 16 mounted thereon. Mounted on the upright 14 is a double-acting reciprocatory fluid pressure motor, generally designated 18, and consisting of a cylinder 20 having service ports and pipes 22 and 24 near its oppof site ends adapted to be connected to a source of cornpressed air or hydraulic fluid by Way of a conventional four-way control valve (not shown). Reciprocably mounted in the cylinder 20 is a piston 26 carried on a piston rod 28, the outer end of which carries a toothed rack 30 meshing with a pinion 32 pinned or otherwise drivingly secured as at 34 to a crankshaft 36 (Figure 3). The crankshaft 36 is journaled in a horizontal bore 38 in the second upright 15 rising from the base 12 and spaced apart from the uprights 14 and 16.

Pinned or otherwise drivingly secured to the opposite end of the crankshaft 36 from the pinion 32 is the hub 42 of a' crank 44, the outer end 46 of which is drilled to receive a pin 48 which is mounted in a hole 50 in one of a pair of parallel links 52 and 54. The parallel llinks 52 and 54 at their lower ends are pivotally mounted upon spaced pivot pins 56 and 58 (Figure 4), which in turn are seated in a slide block 60. The slide block 60 is provided with a vertical bore 62 (Figure 3) by which it is slidably mounted upon a vertical shaft 64, the lower end of which is seated in a hole 66 in the base 12 and the upper end in a bore 68 in an arm 70 projecting `lat erally from and integral with the upright 16. A stop pin 72 is preferably provided on the upright 16 at the lowest point of travel of the slide block 60 (Figure 4) The free ends of the parallel links 52 and 54 are provided with spaced holes 74 and 76 respectively adapted Figure 8 aview similar to Figure 4, but showing a i to receive pivot pins 78 and 80 spacedly mounted in the rearward end of a horizontal arm 82, lwhich is thereby provided with a length-of-stroke adjustment depending upon which of the pairs of spaced holes 74 and 76 is occupied by the 4pivot pins 78 and 80 respectively. The forward end of the arm 82 is provided with a horizontally-bored depending boss 84 slidably receiving the supporting rod 86 of a workpiece gripping jaw appliance, generally designated 90, which is locked in its adjusted position by the set screw 88. The gripping jaw appliance 90 in addition to the rod 86 includes a bracket 92 pinned or otherwise secured as at 94 to the rod 86 and bored as at 96 at its lower end to receive the forward end of a double-acting reciprocatory fluid pressure motor 98. The motor 98 consists of a double-acting cylinder 100 having service ports and pipes 102 and 104 Ylocated near its opposite ends andfadapted to be connected to a source of compressed air or hydraulic fluid by -way of a conventional fourway control valve (not shown). Reciprocably mounted in the cylinder is a piston 106 carried by a piston rod 108, the forward end of which carries a connection block which is pivoted as at 112 to an arm 114 depending from a slide 116 having a bore 118 slidably engaging the rod 86. Pinned 'or otherwise secured as at 120 lto the outerendof the rod 86 is a cam 3 block 122 having an inclined jaw-operating cam surface 124.

Extending forwardly from the depending arm 114 of the slide 116 is a horizontally-projecting stationary arm 126, the outer end of which carries an integral stationary workpiece-gripping jaw 128. Located intermediate the depending arm 114 and the stationary jaw 128 is a downwardly-extending lug or boss 1311 in which is mounted a pivot pin 132 pivotally supporting a movable jaw lever 134, the outer end of which is provided with a workpiece gripping jaw 136. The opposite end of the lever 134 is provided with an upwardly-extending cam follower 138 which is engageable with the cam surface 124 when the slide 118 moves forwardly to the forward end of its stroke, closing the movable jaw 136 upon the lip or other portion L of a workpiece W and forcing it into tight engagement with the stationary jaw 128.

In the operation of the workpiece handling device of Figures 1 and 4 inclusive and 6, let it be assumed that the workpiece W has been pressed or stamped from a piece of sheet metal between an upper die or punch 140 attached to the platen of a conventional press (not shown) and the inner and outer members 142 and 144 of a lower die 146. Let is also be assumed that the lower die 142 has as die cavity 143, and the upper die 140 a punch surface 145, also that the upper die or punch 140 has been retracted and the inner member 142 of the lower die 146 has been raised to eject the workpiece W to the position shown in Figure 1. Let it be further assumed that air or other pressure iiuid has been admitted through the pipe 24 to the forward end of the cylinder 20 of the reciprocatory motor 18, moving the piston 26, piston rod 28 and rack 30 to the left and consequently rotating the pinion 32 and crank 44 in a clockwise direction. This action swings the parallel links 52 and 54 and the arm 82 from the dotted line position to the right to the solid line position of Figure l. At the same time, the workpiece gripping appliance 90 is moved to the right, actuating a limit switch (not shown) which in turn causes the four-way control valve (not shown) of the motor 98 to be reversed, consequently reciprocating the piston 106 and rod 108 to move the fixed and movable jaws 128 and 136 of the workpiece gripping appliance 90 from the dotted line position to the right to the solid line position of Figure 1. When the cam follower 138 arrives at the cam block 122 and engages the cam surface 124, it rocks the jaw lever 134 and moves the movable jaw 136 upward into engagement with .the workpiece lip L at thekprecise instant it arrives beneath the latter, grasping the workpiece W at its lip L between the Stationary and movable jaws 128 and 136. This is `the position of the parts as shown in Figures 1 to 4 inclusive and 6.

The four-way valve (not shown) controlling the reciprocatory motor 18 is now reversed by supplying pressure fluid to the opposite service pipe 22 (Figure l), causing the piston 26 and rack 30 to move to the right, rotating the pinion 32 and crank 44 counterclockwise so as to swing the parallel links 52 and 54, arm 82 and workpiece gripping appliance 90 upward and rearward to the left from the solid line to the dotted line positions of Figure 1. The upper pivot pins '78 and 80 of the parallel links 52 and 54 pursue upwardly-arched paths of travel indicated by the arcuate dotted lines 148 and 150 respec tively, thereby causing the jaws 136 and 128 to travel a similar upwardly-arched path.

When this occurs, the entire workpiece-gripping appliance 90 travels through a similar arcuate path, and the workpiece W is lifted upwardly out of the die cavity 143 in an arcuate path and deposited in the dotted line position of Figure l upon a receiving member 152, such as a conveyor belt. While this is occurring, the limit switch (not shown) controlling the four-way valve (not shown) which in turn controls the jaw-actuatingv motor 98, is shifted to supply pressure uid to the service pipe 104, retracting the piston 106, piston rod 108, slide v118 and movable jaw lever 134 to the left, withdrawing the cam follower from the -inclined cam surface 124, as shown in the dotted line position in the central portion of Figure l. When this happens, the movable jaw lever 134 rocks on its pivot pin 132, swinging the movable jaw 136 away from the stationary jaw 128 so as `to relinquish their grip upon the lip L of the workpiece W, releasing the workpiece W as it arrives upon the receiving member 152.

In this manner, the workpiece handling device 10 can be 'operated automatically to gripand remove the workpiece W from the dies 140 and 146 in timed relationship therewith, and this operation can be accomplished automatically by suitable conventional means used in so-called automation set-ups. The workpiece handling devices 10 of the present invention thus can be arranged to serve a battery of stamping presses and to remove workpieces therefrom without the intervention of human hands at precisely-controlled -times and to precisely-determined positions. v

Figure 6 illustrates how the path of travel 148 or 150 of the pivot pins 78 and 811 of the parallel links 52 and 54 and consequently the path of travel of the gripping jaws 128 and 136 may be varied by lengthening the crank 44 as at 44a and shifting the crankshaft 36 to a new location designated 36a. While the crank pin 48 of the lengthened crank 44a is pursuing its arcuate path of travel 154 around the newly-located crankshaft 36a, the pivot pin 78 travels along a new arcuate path of travel 156 (Figure 6) from a low point or pickup point 158 to a high point or release point 160. In this manner, the workpiece handling device 10 of Figure l may be caused to pick up a workpiece W at a low level position of the jaws 136 and 128 corresponding -to the position of the pivot pin 78 and release the workpiece at a higher level at a point corresponding to the point 161) brut of course spaced horizontally to the right thereof by a distance equal to the distance between the pivot pin 78 and the jaws 128 and 136 in Figure 1. It will be observed that the central portion of the arm 812 (Figures 1 and 2) has been omitted to shorten the horizontal extent of the drawings. Thus, in Figure 6, the workpiece receiving member 152 maybe located on a level higher than the mold cavity 143 rather than on or slightly below that level, as shown in Figure l.

The modied or ceiling-mounted workpiece handling device, generally designated 170, shown in Figures 5 and 7, is in substance an inversion of the Hoor-mounted workpiece handling device 10 of'Figures 1 to 4 inclusive and `6 and corresponding parts carry the same reference numerals. In Figure 5, the lengths of the three yuprights 14, 15 and 16 have been extended to provide free swinging of the crank 44 and to provide `a suiiicient upward length of stroke of the slide block 60 into the dotted line position shown in Figure 5. The stop pin 72 has been moved to the opposite side of the slide lblock 60 so as to lie below the previous upper end of the slide block 60, now the lower end thereof, due to the inversion of the apparatus. The links 52 and 54 and the arm 82, as well as the workpiece gripping appliance 90, remain the same, together with the workpiece receiving member 152.

In the operation of the overhead-mounted workpiece handling device '170 of Figures 5 and 7, the apparatus is actuated in the manner described above in connection with the workpiece handling device 10 shown in Figures l to 4 inclusive, in order to grip the lip L of the workpiece W Yand lift it out of the die cavity 143, carry it tothe left in an upward path of travel, and deposit it rupon the workpiece receiving member 152, such asa conveyor belt. At the same time, the 'workpiece-gripping jaws 128 and 134 are opened automatically in the above-described manner to release the workpiece W upon the workpiece receiving member 152 as before. During the operation .of the overhead-mounted workpiece handling device 170, however, vthe slide block 60 moves in the opposite direction from its previous direction of travel in Figures 1 to' 4 inclusive, causing the pivot pins 56 and 58 to move toward the base 12 rather than away fromit, as in Figure l. As a consequence, the pivot pins 78 'and 80 of the parallel links 52 and 54 pursue paths of travel corresponding to the dotted arcuate line 172 of Figure 5 roughly resembling the shape of an archers bow, having reverse- 1y curved ends. This path of travel 172 has rather sharply dened rises at its-starting and stopping points, with a concave arcuate path of shallow camber inter;- mediate the end rise points..

The arrangement shown in Figure 5 represents an overhead-mounted workpiece handling device with a shorter crank 44 .than would ordinarily be used, because more sharply defined rises are ordinarily required in. order to lift a workpiece clear of all but the lvery shallow die cavities. Figure 7 shows the effect of lengthening the crank 44 of Figure 5 and also of shifting the location Vof the crankshaft 36 of the lengthened crank.` In the solid line position of the lengthened crank, here designated at 44b, the crankshaft 36 is located, as before, immediately and vertically below the pivot pin 56. The path of the crank pin 48h is indicated by the lightly-dotted arcuate line 174, whereas the path of travel of the pivot pin 78 at the free. end of the link 52 is indicated by the lightlydotted line 176. It will thus be seen that this path of travel 176 which also corresponds to the path of travel of the workpiece gripping jaws 128 and 136, has sharp rises at the initial `and terminal endsl of the path, and an arched or convex path of travel between these end rises. This makes the solid-line crank arrangement of Figure 7 desirable fort'aking a workpiece out of a die with a deeper die cavity than that shown at 143 in Figure 5, and depositing it ata position ylevel with a precisely-located point 78b on the same level.

On the other hand, the overhead-mounted workpiece handling device 170 of Figure 5 may also be used to pick up -a workpiece on one level, lift it out of a die cavity and transfer it upward to a precisely-located point of deposit upon a higher level, as indicated by the heavily-dotted lines in Figure 7. In this situation, the crank 44 has been not only lengthened but shifted upward so Ilthat the crankshaft 36 is located to one side of a vertical line dropped fromthe pivot point 56 to which the link 52 is pivoted, the lengthened crank 44a heing also connected to the link 52 but at a location 48a` nearer its pivot 56. iAs before, vthe crank pin 48C pursues a circularlyarcuate path of travel 178, whereas the free end pivot pin '.78V of the link 52 pursues a path vof travel 180 which has a sharp initial risc followed by a continuing gradual rise to the approximate midpoint of the path 180 in a generally.

shallow convex lline; but Abeyond the midpoint the path of travel continues upward in a shallowly concave line to the terminal point 78C at a higher level thanrthe initial point 78. In this heavy line arrangement of Figure 7, therefore, by relocating the crank and relocating the crankshaft to the locations 44C and 36e respectively, a workpiece may be faken out of a fairly deep die cavity and gradually lifted in a shalllowly ascending path to a position level with a point of deposit 7 8`c on a higher level from the point of pickup 78. Here, of course, the path traveledby the jaws 136 and 128 is the same as the path- 180, but displaceda considerable distance to the right. In order to give a compact showing of the paths oftravel, the path of travel of the pivot 78 has been selected because it corresponds to the path of travel of the jaws 128 and 136 while being closer to the crank 44, 44a, 44b or 44e which produces the particular path of travel under discussion.

The further modified workpiece handling device, generally designated 190, shown in Figure 8 consists of a base or mounting structure 192 which, of course, can be inverted and supported from overhead or on its side, and which has a projecting portion 194 carrying a pivot member 196 upon which la swinging arm 198 is pivotally mounted to swing toward and away from the base 192 in response `to the oscillation or swinging of a crank 200 mounted upon a crankshaft 202 as in the manner previously described in connection with Figures 1 and 5, and carrying a pivot pin or crank pin 204 at its outer end pivotally connected t0 one of a pair of the spaced approximately parallel links 52 and 54 of the previously-described forms of the invention. These links 52 and 54 are pivoted, as before, by pivot pins 56 and 58 to the link support 60 whichhere is attached to' or integral with the arm 198.

Asl before, the pivot pins 78 and 80 connect the outer ends of the links 52 and 54 to the oscillating arm 82, whichl in turn carries a workpiece holder, such as the workpiece gripping appliance 90 previously described.

, The hase 192 carries a stop 206 which limits the path of reciprocation of the swinging arm 198 and link support 60 in a direction toward thebasc 192.

In the operation of the workpiece handling device 190, the crankshaft 202 is "oscillated, as by connecting it through a conventional exible coupling (not shown) to the rack and pinion mechanism 30, 32 of a reciproca-tory fluid-pressure motor 18 (Figures l to 3 inclusive), the consequent swinging of the crank 200 in an arcuate path away from the base 192 causing the links 52 and 54 to swing to and fro, while at the same time the link support 60 and the arm 198 are caused to swing upward and downward around'the pivot member 196. The result is that the work handling member or arm 82 and the work grip-v Yper or other work holder attached thereto is caused to travel in a path having initial and final rises in a manner roughly approximating the path of travel of the correspending elements in Figures 1 and 2. It will also be evident that by lengthening lthe projection 194, the base 192 may be mounted overhead in a mannerv analogous to Figure 5, and the crank 200 swung in an arc toward the base 192 in a manner analogous to Figure 5.

The modified workpiece handling device, generally designa-ted 210, shown in Figure 9 consists ofa base 212 upon which la link support =214 is rixedly or stationarily mounted. As before, -a crankshaft 216 is supported from any suitable structure, such as that shown in Figures 1 to 3 inclusive, and oscillated .by mechanism similiar to that shown therein, or by other suitable means. The links 52 and 54 are, las before, supported upon pivot pins 56 and 58 in approximately parallel relationship, but motion is transmitted to one of the links, such @as the link 52, by a pin-and-slot connection, generally designated 218, and consisting of ya slot 220 which is engaged by the crank pin 222 on theouter end of the crank 224 which in turn is mounted for oscillationon the oscillatable crankshaft 216. A workpiccehandling larm or member K82 (not shown) is mounted on the outer ends of the links 5-2 land 54, in a -m'anner similar to that shown in Figure 8, by similar pivotal connections 78 and 80 thereto, Iand ,a workpiece holder, such as the workpiece gripper 90 of Figures lI and 2 is mounted on the workpiece handling arm `8-2.-

4In the oper-ation of the further modiiied workpiece handling device 210, the crankshaft 21-6 is oscillated and the crank 224 swung to and fro by suitable mechanism, such fas that shown in Figures 'l and 2, with the resuit that the crank pin 222 swings in an arcuate path away lfrom the base 212. By reason of this motion, it transmits a swinging motion to the Iapproximately parallel links 52 :and 54 Iby the `engagement of the crank pin 222 with the elongated slot 220. In place of the slot 220, a groove or one or more guide ribs may equally well be used. The consequent swinging of the links 52 and 5'4 around their pivots i56 and 58 causes the upper ends of the links 52 and 54 and their pivot pins 78 and 80 to travel along |arcuate-paths centered at the pivot pins `56 and 58. As 4a consequence, the workpiece holder, such as the workpiece gripper 90, mounted on the workpiece handling .arm or member 82 also travels in a similar arcuate path along a radius equivalent to the distance between the pivots 56 and 78 or 58 and 80.

While the present invention has been described, for

purposes of illustration, with respect to the unloading of workpieces Vfrom Ia machine, it will be evident that it is -alsoapplicable by the Vuse of multiple workpiece handling devices .of thepresentinvention arranged in sequence, to the transfer of workpieces by leapfrog motions from place to place. The wonkpiece handling device may also be used `for the yfeeding of workpieces to a machine, or to the manipulation of articles by remote control, such as radio-active articles behind shielding.

The workpiece gripper 90 is conventional and available upon the market, hence its details are outside the scope of the present invention. This workpiece gripper 90 has been described and shown clearly for purposesof ex- .ample and not by way of limitation. It will be obvious that any other suitable type of workpiece holder can be used, such as a suction cup, a magnet for ferrous metal articles or -articles having ferrous portions, or av direct lift device, such asV forklift lingers.

The terms door and ceiling have been used in a purely relative manner herein, and not by way of limitation. Many press rooms, for example, have no ceiling within reach, in which case the workpiece handling device of the present invention is mounted upon a bracket extending outward from the upper portion of the press itself or from a vertical stanchion or pillar, or on a bracket depending from overhead building structure.

It will also be evident that the workpiece handling device of the present invention is adapted to be mounted with the base 12, 192 or 212 in any suitable position according to the requirements of the particular installation, such as vertically, horizontally or on an incline. The terms vertical and horizontal have thus seen used in a purely relative sense and not by Way of limitation because the meaning of these terms becomes reversed when the base itself is mounted in a vertical position rather than a horizontal position. When the base is mounted in a vertical position, the vertical oscillation of the workpiecev handling member 82 permits the invention to be used for a vertical workpiece handler or elevator. The term floor-mounted also means supported from below rather than any necessity for mounting the invention directly upon a stanchion or support resting upon the floor. Whatever the manner of mounting the base 12 or 192, as the case may be, it will still be true that the direction of oscillation of the workpiece handling member or arm 82 will be approximately perpendicular to the direction of oscillation of the link supporting member 66 or 190.

When, for example (Figures 10 and 1l), the workpiece handling device of the present invention is used for transfer of workpieces from place to place by the leapfrog motion mentioned above, a combination of the motions imparted to the workpiece holder in Figures 1 and 5 may be employed in order to avoid the necessity of waiting for the workpiece to be removedfrom its place of deposit before the workpiece holder returned to its pickup position. In other words, the crankshaft 36 is caused to rotate, moving the crank 44 and the crank pin 48 in a circular path, causing the outer ends of the p-arallel links 52 and S4 to travel in an arched path during their pickup and forward stroke, but to return in an approximately rectilinear or slightly concave path upon the return stroke. This motion per revolution of the crankshaft 36 is illustrated by the arcuate path 148 of Figure 6 for the forward stroke and the bow-shaped path 172 of Figure 5 for the return stroke. Under these circurn.- stances, of course, the stop 72 would be removed -so as to permit full rotation of the crankshaft and crank.

' Under suitable circumstances, the workpiece handling device ofthe present invention may be used for transfer of workpieces by. omitting the workpiece `gripping appliance and causing the workpiece handling element or arm 82 to pick up the workpiece either directly or by engaging the bail or handle of a receptacle, such as a basket, containing the workpiece or workpieces. Alternatively, a workpiece handling element 82 vmay be bifurcated so as tocprovide'a workpiece-lifting fork which is inserted beneath the workpiece to lift and transfer. it. Furthermore, the projecting or overhanging portion which constitutes the major part of the arm 82 maybe shortened or even be omitted entirely, and the work holder or work rest may be mounted on or near the outer ends of the links 52 and 54. The links 52 and 54 then require only a short link between them to transmit motion and support the work holder. Optionally, the wo-rk holder can be omitted and the work lifted directly by this short-link vestige of the larm 82.

What I claim is:

A workpiece handling device comp-rising a mounting structure, a link-supporting member mounted on said structure for reciprocating motion relatively thereto, means on said structure for guiding said supporting member in reciprocation between predetermined opposite positions, a pair of elongated approximately parallel link members pivotally connected lat their inner ends to said supporting member for motion to and fro relatively thereto, a workpiece handling element pivotally connected to the outer ends of said link members in transverse relationship therewith, a workpiece holder mounted on said workpiece handling element, and mechanism including a crank rotating device mounted on said structure and a crank connected to said rotating device and pivotally connected to one of said link members for simultaneously reciprocating said supporting member and swinging said link members to and fro relatively to said supporting member, said ycrank rotating device and said crank being constructed and arranged to move said crank in an arcuate path curved away from said mounting structure during swinging of said link members in one direction and in an arcuate path curved toward said mounting structure during swinging of said link members in the opposite direction whereby to cause said work holder to advance along one path of travel but to return along a different path of travel.

References Cited in the file of this patent UNITED STATES PATENTS v1,556,695 Kronborg Oct. 13, 1925 1,766,573 Westin June 24, 1930 1,835,579 Westin Dec. 8, 1931 1,959,512 Wall May 22, 1934 2,275,561 Sahlin Mar. 10, 19,42 2,609,776 Sahlin Sept. 9, 1952 FOREIGN PATENTS 511,478 Belgium June 14, 1952 

